Control circuit for a controlled electro-magnetic valve of an automotive braking system

ABSTRACT

A control circuit for a controllable electric solenoid valve of a brake system of a motor vehicle is described, in which the actual values of a controlled variable (f(t)), e.g., the vehicle deceleration, a wheel slip, a driving speed, an angle of rotation or the like are returned to a predetermined tolerance band. The actual value of the controlled variable is measured continuously and compared with the predetermined tolerance band, which is stored in an EEPROM, for example. If the actual value of the controlled variable leaves the predetermined tolerance band ( 22 ), a correction device ( 15 ) intervenes and returns the actual value to the predetermined tolerance band by increasing or decreasing the trigger current for the solenoid valve ( 1 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a controllable electric solenoidvalve of a brake system of a motor vehicle according to the preamble ofthe main claim.

[0002] German Patent Application 43 05 488 A1 has already described acontrol circuit for a solenoid valve. With this control circuit, thetrigger current for the solenoid valve is controlled so that the valveclosing body is braked shortly before being moved from its flow-throughposition to its closed position. This yields the result that thesolenoid valve closes with very little noise and thus interfering soundwaves are not transmitted through the brake system to the motor vehicle.The virtually noiseless closing is achieved by briefly turning off thetrigger current to support the valve closing body in the end positionwith a holding current.

[0003] German Patent Application 197 07 960 A1 also describes a methodand a device for regulating the pressure in a wheel brake, a regulatorfor pressure regulation forming a trigger signal from the pressurerelationships prevailing at the valve arrangement. To improve thequality of regulation for the pressure regulation in the brake circuit,one valve arrangement is provided for pressure buildup and another forpressure reduction. By measuring the actual brake pressure and comparingit with the setpoint pressure, a difference is determined and taken intoaccount with an altered trigger signal. The relationship between thetrigger signal and the pressure relationships is stored as acharacteristic curve for the pressure buildup and/or pressure reduction.

ADVANTAGES OF THE INVENTION

[0004] The control circuit according to the present invention for acontrollable electric solenoid valve in a brake position system of amotor vehicle having the characterizing features of the main claim hasthe advantage over the related art that a regulator monitors the actualvalue of the controlled variable in question and optionally takes acorrective measure. It is especially advantageous here that thecontrolled variable for the actual value is always within apredetermined tolerance band. If the actual value leaves thepredetermined tolerance band, a correction device additionallyintervenes, returning the actual value to the range of the toleranceband through an appropriate change in the trigger current of thesolenoid valve. This advantageously yields the result that in a brakesystem, for example, quiet or virtually noiseless closing of thesolenoid valve is achieved, while on the other hand, the brake pressurein the brake circuit is adjustable independently of the function of theregulator.

[0005] Advantageous refinements of and improvements on the controlcircuit characterized in the main claim are possible through themeasures characterized in the dependent claims. It is particularlyadvantageous that the correction device is designed to alter the fieldcurrent as a function of the closing force of the solenoid valve.Through appropriate characteristic curves determined empirically inadvance, the closing force of the valve closing body is adjustable atwill and is selected by taking into account the pressure in the linesystem, so that the closing body, for example, does not open when thereis an increase in the line pressure due to an altered controlledvariable. For example, if a current/pressure characteristic curve (I/Pcharacteristic curve) has been stored as the controlled variable, thenthe control current for a certain pressure value may be obtained toadvantage according to the characteristic curve.

[0006] It is also advantageous that to regulate the driving dynamics orthe brake performance of a vehicle, for example, the brakingdeceleration, the vehicle speed and/or wheel slip values may be selectedas the controlled variable. These controlled variables are needed inparticular for an antilock brake system (ABS) or the ElectronicStability Program (ESP).

[0007] It is also advantageous that the correction device forms a brakeintervention measure in combination with Adaptive Cruise Control (ACC),as is also used in combination with a speed regulator, when the setpointvalue for the distance is too low for safety reasons with respect to thedriving speed.

[0008] A memory is advantageously provided for storing thecharacteristic curves for the controlled variable and/or the toleranceband. A suitable memory is preferably an EEPROM, because this memorydoes not lose its information even in a power failure.

[0009] An advantageous implementation also involves the correctiondevice having a computer which calculates the actual value by using asoftware program. Software programs have the great advantage that theyare easily modifiable without requiring complex wiring. In particular,in a motor vehicle having an antilock brake system or a driving dynamicsregulator, this yields the advantage that correction of the controlledvariable is easily implementable through a corresponding expansion ofthe existing control programs.

DRAWING

[0010] One embodiment of the present invention is illustrated in thedrawing and explained in greater detail in the following description.

[0011]FIG. 1 shows an electric solenoid valve in an open flow-throughposition.

[0012]FIG. 2 shows an electric solenoid valve in an closed position.

[0013]FIG. 3 shows a block diagram.

[0014]FIG. 4 shows a diagram.

DESCRIPTION

[0015] For a better understanding, FIGS. 1 and 2 show an electricsolenoid valve 1 in which a valve closing body 4 is shown in the openedposition (FIG. 1) and in the closed position (FIG. 2). Solenoid valve 1has a valve body 2 in which valve closing body 4 is situated inside abore. Valve closing body 4 is designed in the lower part so that ahollow space is formed between the inside wall of valve body 2 and valveclosing body 4, so that brake fluid is forced into this hollow space inthe case of a brake system, for example. Closing body 4 is sealed at thetop with respect to the inside wall of valve body 2. Closing body 4 isheld in its basic position, preferably in the opened position accordingto FIG. 1, by one or more springs 3. In the upper area, a suitablesolenoid M (not shown in detail) through which a field current flows ismounted on valve body 2. The magnetic force which develops acts on valveclosing body 4 with a magnetizing force F_(Mag) against spring forceF_(F) as indicated by the direction arrows in FIG. 2. Closing forceF_(K) which acts on the spherical cup and with which outlet A is closedis obtained from the difference between magnetizing force F_(Mag) andspring force F_(F). The closing force is controlled by the field currentfor the solenoid, so that the desired movement and holding force forvalve closing body 4 are achieved.

[0016] The functioning of the present invention will now be explained ingreater detail on the basis of the embodiment according to FIGS. 3 and4. In the case of control of an electric solenoid valve 1, the essentialproblem occurs that manufacturing tolerances, e.g., the size of theresidual air gap between valve body 2 and the driving magnet,temperature effects, friction effects and wear may lead to differentclosing forces at the same trigger currents for the solenoid. Thetrigger current thus depends not only on the differential pressure overthe valve but also the unwanted side effects mentioned above. Apredetermined current/pressure characteristic curve (I/P characteristiccurve) for triggering valve closing body 4 therefore necessarily leadsto different closing forces F_(K) which may then be compensated throughan increase or decrease in the corresponding control current. However,increasing or decreasing the control current by regulation yields anunwanted time lag which is not desirable with the short reaction timesthat are required. For example, in the case of driving dynamicsregulation, when the vehicle begins to swerve, it must be possible tobrake the corresponding wheel of the vehicle through, if possible, animmediate brake response in order to stabilize the driving condition.Therefore, lengthy reaction times are unacceptable.

[0017] Therefore, the implementation according to the present inventionas shown in FIG. 4 is based on the fact that controlled variable f(t)which is to be controlled and/or regulated is measured continuously. Inthe case of an antilock brake system (ABS) or a vehicle regulator havingan electronic stability program (ESP), the controlled variable may bethe vehicle deceleration, a wheel slip, the driving speed, an angle ofrotation or some other dynamic parameter which determines the drivingresponse. Controlled variable f(t) is preselected as a setpoint value inthe time diagram in FIG. 4. In addition, a tolerance band 22 withinwhich the actual value for controlled variable f(t) may vary is givenfor controlled variable f(t). The tolerance band runs about the setpointvalue, i.e., a setpoint value with a time lag. In normal operationwithin the tolerance band, the normal regulator operates with thedesired comfort and harmonious coordination. Outside the tolerance band,the measure taken to intervene in the regulation is preferably moreforceful and more severe.

[0018] The values for controlled variable f(t) and/or tolerance band 22are stored in a suitable memory, e.g., an EEPROM, in the form of atable, a characteristic curve or in some other suitable form, and thusthey may be accessed by regulator 11 at any time. Tolerance band 22 maybe determined empirically or according to a worst case analysis.

[0019] In driving operation, regulator 11 according to FIG. 4 attemptsto regulate actual value 24 in accordance with the measured systemdeviation so that it is within the given tolerance band 22. According toFIG. 3, regulator 11 determines system deviation 17 continuously andderives a suitable control value for triggering hydraulic system 12, 13from stored tolerance band 22. A hydraulic system 13 then increases thepressure in the brake system, for example, and thus increases thedeceleration of vehicle 14. The actual deceleration is then measured andsystem deviation 17 is again determined from that.

[0020] If the actual value for controlled variable f(t) is outside oftolerance band 22 according to the left-hand portion of the diagram inFIG. 4, then a correction device 15 intervenes and returns the actualvalue 24 of the controlled variable to I/P characteristics map 16 byincreasing the trigger current for electric solenoid valve 1, forexample. Then regulator 11 again assumes the triggering of hydraulicsystem 12, 13 on the basis of the stored engine characteristics map.With the help of correction device 15 an adaptive correction of thecontrol characteristic is then performed. As an alternative, forexample, in the right-hand portion of FIG. 4, a reduction in the triggercurrent is necessary because the actual value is below tolerance band22.

What is claimed is:
 1. A control circuit for a controllable electricsolenoid valve of a brake system of a motor vehicle for adjusting aholding force for a valve closing body (4) of the solenoid valve (1) andhaving a regulator (11) which predetermines the field current for thesolenoid valve (1) according to the setpoint value of a predeterminedcontrolled variable (f(t)), wherein the regulator (11) regulates orcontrols the actual value (24) of the controlled variable (f(t)) withina predetermined tolerance band (22); in addition, a correction device(15) is provided; and the correction device (15) is designed to increaseor decrease the field current when the actual value (21) leaves thepredetermined tolerance band (22) for the setpoint value of thecontrolled variable (f(t)).
 2. The control circuit as recited in claim1, wherein the correction device (15) is designed to alter the fieldcurrent as a function of the closing force (F_(K) ) of the electricsolenoid valve (1).
 3. The control circuit as recited in claim 1 or 2,wherein the correction device (15) preselects a current/pressurecharacteristic curve (I/P characteristic curve) as the controlledvariable (f(t)).
 4. The control circuit as recited in one of thepreceding claims, wherein the correction device (15) is designed tocorrect the actual value of the braking deceleration.
 5. The controlcircuit as recited in one of the preceding claims, wherein thecorrection device (15) is designed to correct the actual value of thevehicle speed.
 6. The control circuit as recited in one of the precedingclaims, wherein the correction device (15) is designed to correct theactual value of a wheel slip value.
 7. The control circuit as recited inone of the preceding claims, wherein the correction device (15) isdesigned to perform a brake intervention measure in conjunction withAdaptive Cruise Control (ACC) when the value drops below a setpointvalue for the distance from an obstacle.
 8. The control circuit asrecited in one of the preceding claims, wherein a memory, preferably anEEPROM, is provided in which correction values for the trigger currentare stored as a function of the setpoint value of the controlledvariable (f(t)) and/or the tolerance band (22).
 9. The control circuitas recited in one of the preceding claims, wherein the correction device(15) has a computer which calculates the actual value of the controlledvariable (f(t)) by using a software program.
 10. The control circuit asrecited in one of the preceding claims, wherein the correction device(15) is designed to control an antilock brake system (ABS) and/or anelectronic stability program (ESP).